Respiratory motion management is a common challenge for many MR thoracic and abdominal applications. A breath-hold is typically 10-20 seconds, however most MR measurement sequences take much longer to complete. Therefore, motion needs to be carefully controlled in such applications for diagnostic quality imaging. In the case of diffusion weighted imaging (DWI) the acquisition of a single image is relatively fast compared to a breathing cycle, however the signal to noise ratio of a single acquisition is typically too low for diagnosis. While averaging multiple acquisitions can effectively improve signal to noise ratio, critical structure edges are also blurred if significant motion is present during the acquisition.
For clinically desired image quality, respiratory triggered MR sequences are used as the current state-of-art approaches to address the motion beside simple averaging with the associated loss in sharpness. Triggered acquisitions come at the expense of extended scan time. Furthermore triggering requires an additional hardware device such as a respiratory belt or additional acquisition modules. For instance, Siemens Magnetom Trio provides the Physiological Measurement Unit (PMU) as an option to control MR sequence using a patient's physiological signal, including respiration.